Process for the conversion of steroidal



United States Patent George P. Mueller, Park Ridge, 111., assignor to G. D.

Searle & Co., Chicago, 111., a corporation of Delaware No Drawing. Application January 26, 1956 Serial No. 561,656

11 Claims. (Cl. 260-3974) The present invention relates to improvements in processes for the conversion of steroidal sapogenins to nuclearly-unsaturated pregnane derivatives, and is particularly concerned with improvements whereby the nuclearly-unsaturated pregnane derivative is obtained without isolation of a reaction product at any of the intermediate stages of the degradation.

It is known in the art that the conversion of steroidal sapogenins to pregnane derivatives can be achieved by various multi-stage operations characterized by the isolation of certain of the intermediate products obtained therein. Such multi-stage operations, or individual steps thereof, have been disclosed by Marker and coworkers, U.S. 2,352,850, 2,352,851, and 2,352,852; by Gould and Hershberg, U.S. 2,632,008; by Rust, U.S. 2,623,053; by Wall, U.S. 2,666,770; and by other workers. 'Prior to the present invention, however, the advantages derivable from conducting the entire degradation in a manner which permits its completion without the isolation of a single intermediate product have not been realized. In fact, the different solvents required, as well as the diversity of reagents employed, would lead to the expectation that a sapogenin degradation conducted without isolation of any intermediate product would result in the formation of a multiplicity of by-products and little or none of the desired product.

It has now been found, in accordance with the present invention, that unexpectedly beneficial results, both with respect ,to simplicity of operations and yield of the desired product, are obtained by conducting the degradation as described herein. Steroidal sapogenins, including esters and ketonic derivatives thereof, are generally applicable for use in the processes of this invention. For example, one may employ as starting materials such compounds as sarsasapogenin, smilagenin, tigogenin, neotigogenin, diosgenin, gitogenin, rockogenin, hecogenin, and yamogein as well as stereoisomers, esters and ketonic derivatives related to the foregoing. A preferred type of starting material is the 3- hydroxy or 3-acetoxy sapogenin compound, although other ester derivatives such as the propionate, butyrate, and benzoate are also applicable.

A typical representation of the manner of conducting the processes of the present invention can be illustrated by the conversion of tigogenin to 3fi-acetoxy-16-allopregnen-ZO-one. Tigogenin (or its acetate) is heated with acetic anhydride and pyridine hydrochloride at the reflux temperature of the mixture, whereby isomerization to the pseudosapogenin derivative is effected. The mixture is then cooled, diluted with aqueous acetic acid, and treated with an oxidizing agent such as chromium trioxide. It is preferred to dilute the reaction mixture with aqueous acetic acid prior to the addition of the oxidizing reagent, but it is generally equivalent thereto to achieve the dilution simultaneously with the oxidation by the addition of the chromium trioxide in a more highly diluted aqueous acetic acid solution. The excess Patented May 5, 1959 agent, suitably an alcohol such as methanol, an aldehyde such as formaldehyde, Or an inorganic reducing agent such as sodium metabisulfite. Completion of the degradation process is achieved by heating the resulting mixture with an alkali metal salt of a lower alkanoic acid, such as sodium acetate or potassium acetate.

Modifications of this process are achieved by conducting the operations with other lower alkianoic acid anhydrides, lower alkanoic acids and salts thereof. For the purposes of this disclosure the lower alkanoic acids are defined as those straightand branched-chain aliphatic hydrocarbon carboxylic acids which contain fewer than 9 carbon atoms, and the term consequently includes such compounds as acetic, propionic, butyric, and octanoic acids.

In conducting the reaction of the steroidal sapogenin with a lower alkanoic acid anhydride and pyridine hydrochloride, it is not necessary to heat the reaction mixture at the reflux temperature. The isomerization proceeds fairly, rapidly at a temperature of about 140-150 C., and can be eifected readily at a lower temperature by the use of a longer reaction time.

By suitable selection of the steroidal sapogenin starting material, the nuclearly-unsaturated pregnane derivative obtained as the final product will contain either one or a plurality of nuclearly-located double bonds. The

sterochemical nature of the ring fusion of steroid rings A and B in the pregnane derivative obtained as the final product is also determined by the choice of starting material. The term pregnane derivative is defined herein to include not only the cis compounds of the pregnane series but also the trans compounds of the allopregnane series and the compounds of the 4-pregnene and S-pregnene series. For example, application of the processes of this invention to s-arsasapogenin yields a 3/8-acyloxy-16-pregnen-2O-one whereas tigogenin aflords oxidant is then destroyed by the addition of a reducing a 3B-acyloxy-16-allopregnen-20-one and diosgenin affords a 3,8-acyloxy-5,l6 pregnadien-20-one.

A particular utility of the processes of this invention is that they are especially well adapted for the chemical processing of steroidal sapogenin compositions which are not stereochemically-pure compounds. It is well known that sapogenin preparations obtained from natural plant sources are commonly mixtures, and that components of a single mixture may exhibit stereoisomerism at positions 22 and 25. One of the advantages of the processes disclosed herein is that complications which would otherwise result from the presence of stereoisomers in the mixture are avoided by conducting the degradation without the isolation of any intermediate product. Thus,

considering only the stereoisomerism at positions 22 and 25, a;stereoisomeric 3-hydroxy-sapogenin mixture will have four possible components. On acetylation, these will afford four individual acetates, but conversion of themixture to the pseudosapogenin will yield only two stereoisomers, and treatment of this mixture with chromium trioxide and a reagent such as sodium acetate will yield a stereochemically-pure pregnane derivative. The difiiculties of separating and purifying stereoisomeric compounds are well known in the art, and a particular advantage of the processes described herein is that when crude sapogenin mixtures are employed as starting materials, these tedious separations are avoided, with a resulting increase in the yield of the desired pregnane derivative. In practice it is found that the processes of this disclosure afl'ord desired pregnane derivatives in yields in excess of 65% from stereochemically-impure sapogenin starting materials.

The pregnane derivatives obtained in these degradations are useful intermediates for organic synthesis, and

int-heart.

This invention will appear more fully from the examples Which follow. These examples are set forth by way of illustration only and it will be understood that the invention is not to be construed as limited in spirit or in scope by the details contained therein, as many modifications in materials and methods will be apparent from this disclosure to those skilledin the art. In these examples, temperatures are given in degrees centigrade C.) and quantities of materials in parts by weight.

Example 1 A reaction mixture prepared from 20.6 parts of crude hecogenin acetate, 108 parts of acetic anhydride and 7 parts of pyridine hydrochloride is heated under reflux for 3 hours. The cooled reaction mixture is diluted with 340 parts of acetic acid and 80 parts of water, and further cooled to about 15 C. Over a period of 5-10 minutes, a solution of 12 parts of chromium trioxide in 10 parts of water and 105 parts of acetic acid is added, with stirring. The mixture is stirred for an additional 3 hours, during which time the temperature is gradually allowed to rise to 20 C. With continued external cooling to maintain the temperature at about 20 C. or lower, 7 parts of a 36% aqueous solution of formaldehyde is added, and the mixture is stirred for an additional hour. Sodium acetate (40 parts) is added and the mixture is heated at about 85 C., with stirring, for 1-2 hours. It is then cooled, diluted with 2000 parts of Water and extracted with a total of 1400 parts of ether in 3 portions. The ethereal extract is washed repeatedly with water, with dilute sodium bicarbonate solution, and with sodium chloride solution, and is then dried and concentrated. The crystalline residue is crude 3j8-acetoxy-16-allopregnene-12,20-dione of the structural formula omooo Example 2 Example 3 Five parts of crude tigogenin is heated under reflux for 40 minutes with 27 parts of acetic anhydride.

Pyridine hydrochloride (1.5 parts) is added, and the mixture is heated under reflux for an additional 3 hours.v

There are then added to the cooled mixture 85 parts of acetic acid and 20 parts of water, after which the mixture is further cooled to about 15 C. and, with stirring, treated over a period of about 20 minutes with a solution of 3 parts of chromium trioxide, 2.5 parts of water and 28 parts of acetic acid. Stirring is continued for an additional 3 hours, during-which time the temperature gradually rises to about 25 C. The mixture is again cooled to 15 C., and 1.75 parts of a 36% aqueous formaldehyde solution is added. After 45 minutes, 10 parts of sodium acetate is introduced into the mixture, and it is heated at about 85 C. for 1-2 hours. The cooled mixture is diluted with 1000 parts of water and extracted with a total of 550 parts of ether in three portions. The ethereal extract is washed several times with water, then with dilute sodium-bicarbonate solution and with sodium chloride solution. It is dried, filtered, and concentrated to aftorda gummy crystalline residue. A solution of this crude product in 45 parts of benzene is poured on a chromatography column prepared from parts of silica. After the column is washed with 950 parts of benzene, elution with a. 5 volume percent solution of ether in benzene afiords the desired product. Recrystallization from ether and from methanol yields purified 3,8-acetoxy-l6-allopregnen-20-one (1fi-dehydroallopregnanolone acetate). This compound has the structural formula CHsCOO- Example 4 By the procedure of Example 3, with the substitution of tigogenin acetate for the tigogenin, there is obtained the same 3p-acetoxy-16-allopregnen-20-one.

Example 5 Ten parts of crude diosgenin is heated for 30 minutes at about C. with 50 parts of propionic anhydride. Pyridine hydrochloride (3.5 parts) is added to the resulting solution of diosgenin propionate, and the mixture is maintained at about 150 C. for an additional 3'hours. There are then added to the cooled mixture parts of propionic acid and 40 parts of water. While the mix ture is maintained at about 15 C. with external cooling, a solution of 6 parts of chromium trioxide, 5 parts of water, and 50 parts of propionic acid is added over a period of 30 minutes. Stirring is continued for an additional 3 hours, during which time the temperature gradually rises to about 25 C. Methanol is added to reduce the excess chromium trioxide. Potassium propionate (28 parts) is introduced into the mixture, and it is heated at about 85 C. for 2 hours. The cooled mixture is diluted with 2000 parts of water and extracted with a total of 1100 parts of ether in 3 portions. The ethereal extract is washed several times with water, then with dilute sodium bicarbonate solution and with sodium chloride solution. It is dried, filtered, and concentrated to afiord a residue of 3,8-propionoxy-5,16-pregnadien-20- one of the structural formula CHaCHzOO 0 Example 6 Stirring is continued for an additional 3 hours, during which time the temperature'gradually rises to about 25 C. Aqueous. formaldehyde is: added-to aeaaut reduce the excess chromium trioxide. Sodium acetate (20 parts) is added and the mixture is heated at about 85 C. for 2 hours. The cooled mixture is diluted with water and extracted with several portions of ether. The combined ethereal extract is washed several times with water, then with dilute sodium bicarbonate solution and with sodium chloride solution. It is dried, filtered, and concentrated to yield 3fi-acetoxy-5,l6-pregnadien-20-one.

What is claimed is:

1. A process for the manufacture of nuclearly-unsaturated compounds of the pregnane series which comprises: heating a 3-oxygenated steroidal sapogenin composition in a reaction mixture with a lower'alkanoic acid anhydride and pyridine hydrochloride until conversion to the pseudosapogenin derivative is substantially complete, oxidizing said pseudosapogenin derivative by cooling said reaction mixture and adding an excess of an aqueous, lower alkanoic acid solution of chromium trioxide thereto, destroying the unreacted excess of chromium trioxide by adding a reducing'agent, heating the resulting mixture with an alkali metal salt of a lower alkanoic acid, and isolating the steroidal product.

2. A process for the manufacture of nuclearly-unsaturated compounds of the pregnane series which comprises: heating a steroidal sapogenin composition which comprises a member of the group consisting of hecogenin, tigogenin, diosgenin, and their lower alkanoic acid esters in a reaction mixture with a lower alkonic acid anhydride and pyridine hydrochloride until conversion to the pseudosapogenin derivative is substantially complete, oxi' dizing said pseudosapogenin derivative by cooling said reaction mixture and adding an excess of an aqueous, lower alkanoic acid solution of chromium trioxide thereto, destroying the unreacted excess of chromium trioxide by adding a reducing agent, heating the resulting mixture with an alkali metal salt of a lower alkanoic acid, and isolating the steroidal product.

3. A process which comprises: heating a steroidal sapogenin composition which comprises hecogenin in a reaction mixture with acetic anhydride and pyridine hydrochloride until conversion to the pseudohecogenin derivative is substantially complete, oxidizing said pseudohecogenin derivative by cooling said reaction mixture and adding an excess of an aqueous acetic acid solution of chromium trioxide thereto, destroying the unreacted excess of chromium trioxide by adding a reducing agent, heating the resulting mixture with an alkali metal acetate, and isolating 3 3-acetoxy-l6-allopregnene-12,20-dione.

4. A process which comprises: heating a steroidal sapogenin composition which comprises tigogenin in a reaction mixture with acetic anhydride and pyridine hydrochloride until conversion to the pseudotigogenin derivative is substantially complete, oxidizing said pseudotigogenin derivative by cooling said reaction mixture and adding an excess of an aqueous acetic acid solution of chromium trioxide thereto, destroying the unreacted excess of chromium trioxide by adding a reducing agent, heating the resulting mixture with an alkali metal acetate, and isolating 3/3-acetoxy-16-allopregnen-20-one.

5. A process which comprises: heating a steroidal sapogenin composition which comprises diosgenin in a reaction mixture with acetic anhydride and pyridine hydrochloride until conversion to the pseudodiosgenin derivative is substantially complete, oxidizing said pseudodiosgenin derivative by cooling said reaction mixture and adding an excess of an aqueous acetic acid solution of chromium trioxide thereto, destroying the unreacted excess of chromium trioxide by adding a reducing agent, heating the resulting mixture with an alkali metal acetate, and isolating 3/3-acetoxy-5,16-pregnadien- 20-one.

6. A process which comprises: heating a steroidal sapogenin composition which comprises tigogenin in a reaction mixture with acetic .anhydride and pyridine hydrochloride until conversion to the pseudotigogenin derivative is substantially complete, oxidizing said pseudotigogenin derivative by cooling said reaction mixture and adding an excess of an aqueous acetic acid solution of chromium trioxide thereto, destroying the unreacted excess of chromium trioxide by adding formaldehyde, heating the resulting mixture with sodium acetate, and isolating 3/3-acetoxy-16-allopregnen-20-one.

7. A process which comprises: heating a steroidal sapogenin composition which comprises tigogenin acetate in a reaction mixture with acetic anhydride and pyridine hydrochloride until conversion to the pseudotigogenin derivative is substantially complete, oxidizing said pseudotigogenin derivative by cooling said reaction mixture and adding an excess of an aqueous acetic acid solution of chromium trioxide thereto, destroying the unreacted excess of chromium trioxide by adding formaldehyde, heating the resulting mixture with sodium acetate, and isolating 3 3-acetoxy-16-allopregnen-20-one.

8. The process for the manufacture of A -unsaturated compounds of the pregnane series which comprises heating a member of the 16-(6-acyloxyisocaprooxy)-20- ketopregnane series with an alkali metal salt of a lower alkanoic acid in a lower alkanoic acid and isolating the corresponding A -pregnen-20-one steroid.

9. A process for the manufacture of 3-acyloxy-l6-allopregnene-l2,20-dione which comprises heating 3-acyloxy- 16-(a-acyloxyisocaprooxy)-allopregnane-12,20-dione with an alkali metal salt of a lower alkanoic acid in a lower alkanoic acid and isolating the product.

10. The process for the manufacture of 3-acyloxy-16- allopregnen-20-one which comprises heating 3-acyloxy- 16-(6-acyloxyisocaprooxy)-allopregnan-20-one with an alkali metal salt of a lower alkanoic acid in a lower alkanoic acid and isolating the product.

11. The process for the manufacture of S-acyloxy- 5,16-pregnadien-20-one which comprises heating 3-acyloxy-16-(E-acyloxyisocaprooxy)-5-pregnen-20-one with an alkali metal salt of a lower alkanoic acid in a lower alkanoic acid and isolating the product.

References Cited in the file of this patent UNITED STATES PATENTS 2,352,851 Marker July 4, 1944 2,352,852 Marker July 4, 1944 2,623,053 Rust Dec. 23, 1952 2,666,770 Wall Jan. 19, 1954 2,716,125 Hirschmann Aug. 23, 1955 

1. A PROCESS FOR THE MANUFACTURE OF NUCLEARLY-UNSATURATED COMPOUNDS OF THE PREGNANE SERIES WHICH COMPRISES: HEATING A 3-OXYGENATED STEROIDAL SAPOGENIN COMPOSITION IN A REACTION MIXTURE WITH A LOWER ALKANOIC ACID ANHYDRIDE AND PYRIDINE HYDROCHLORIDE UNTIL CONVERSION TO THE PSUEDOSAPOGENIN DERIVATIVE IS SUBSTANTIALLY COMPLETE, OXIDIZING SAID PSEUDOSAPOGENIN DERIVATIVE BY COOLING SAID REACTION MIXTURE AND ADDING AN EXCESS OF AN AQUEOUS, LOWER ALKANOIC ACID SOLUTION OF CHROMIUM TRIOXIDE THERETO, DESTROYING THE UNREACTED EXCESS OF CHROMIUM TRIOXIDE BY ADDING A REDUCING AGENT, HEATING THE RESULTING MIXTURE WITH AN ALKALI METAL SALT OF A LOWER ALKONIC ACID, AND ISOLATING THE STEROIDAL PRODUCT. 